The present invention relates to torque limiters for use in various machines such as machine tools in order to prevent transmission of excessive torque between the input side and the output side. More particularly, the present invention relates to an improvement in torque limiter of a type wherein upper and lower projected peripheral edges vertically spaced apart are provided on a cylindrical boss connected to a drive shaft of the input side so as to be rotated integral therewith, a drive flange on the output side is disposed between said pair of projected peripheral edges, a plurality of circumferentially separated recesses are formed in the lower surface of said drive flange at the outer portion thereof and a roller bearing housed in the lower projected peripheral edge is closely fitted into the recess, said roller bearing being elastically pressed into the recess by the action of a torque spring disposed therebelow and set to a predetermined pressure, and the drive flange is rotatably mounted at the inner portion thereof on the cylindrical boss through bearing means.
A torque limiter of this kind is known and disclosed in Japanese Patent Publication No. 21894/80. In this known torque limiter, as the aforesaid bearing means there is provided three-rows bearings comprising needle bearings for receiving a load in a rotational direction of the drive flange, thrust bearings and thrust needle bearings for receiving a load of an axial direction of the drive flange thereby to rotatably mount the flange on the cylindrical boss. However, needle bearings employed in this torque limiter require a cage for holding them, such additional element complicating the bearing structure. Furthermore, the three-rows bearing system for mounting the drive flange on the boss involves a large number of parts and, therefore, assembly of the above torque limiter has been troublesome.